operating and maintenance instructionsRCA Volt-Ohm-Milliammeter Safety Precautions For proper operation, the ground (black) lead of the WV-38A should be connected to the ground of

SUGGESTED PRICE 5Q CENTS

operating and maintenance instructions

R C A Volt-Ohm-Milliammeter

Safety Precautions For proper operation, the ground (black) lead of the W V - 3 8 A

should be connected to the ground of the equipment under test, before any other connections are made. A n important point to remember is that there is always danger inherent in testing electrical equipment. Therefore, the operator should thoroughly familiarize himself with the equipment under test before working on it, bearing in mind that high voltages may appear at unexpected points in defective equipment. Add i tional precautions which experience in the industry has shown to be important are listed below:

1. It is good practice to remove power before connecting test leads to high-voltage points. If this is impractical, be especially careful to avoid accidental contact with equipment racks and other objects which can provide a ground. Working with one hand in your pocket and standing on a properly insulated floor lessens the danger of shock.

2. Filter capacitors may store a charge large enough to be lethal. Therefore, discharge filter capacitors before attaching test leads.

3. Remember that leads with broken insulation provide the additional hazard of high voltages appearing at exposed points along the leads. Check test leads for frayed or broken insulation before working with them.

4. T o lessen the danger of accidental shock, disconnect test leads immediately after test is completed.

5. Remember that the risk of severe shock is only one of the possible hazards. Even a minor shock can place the operator in jeopardy of more serious risks, such as a bad fall or contact with a source of higher voltage.

6. The experienced operator continuously guards against injury and does not work on hazardous circuits unless another person is available to assist in case of accident.

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RCA Volt-Ohm-Milliammeter

Description The R C A WV-38A Volt-Ohm-Milliammeter is a completely portable,

all-purpose measuring instrument. The WV-38A wil l measure rms values of A C sine-wave voltages from 0.1 volt to 5000 volts; D C voltages from 0.005 volt to 5000 volts; D C current from 1 microampere to 10 amperes; resistance from 0.2 ohm to 20 megohms; and decibels from —20 db to +50 db. Input resistance is 20,000 ohms-per-volt on D C , and 5000 ohms-per-volt on A C .

Features of this versatile test instrument include the use of precision resistors in all measuring circuits, and a large, easy-to-read meter with sensitive 50/zA movement. The panel has been specially designed with two-color markings for simplified operation.*

A convenient function switch is provided with A C , + D C , and — D C positions. The + D C and —DC positions of this switch reverse the polarity of the test leads—a feature that is also helpful in checking the front-to-back resistance ratio of electrolytic capacitors and many types of semi-conductor devices.

Two special silicon diodes are used to protect the meter movement against burnout due to accidental overload.* A fuse protects the precision multiplier in the ohms network.

The WV-38A is completely portable, requiring no external power source. Five internal batteries (not provided) are used for the ohms function (4 penlight cells and 1 "D"-size flashlight cell). The unit weighs only 3V2 pounds, and measures 6% inches by 5̂ 4 inches by SVs inches. Convenient clips are provided on the handle for carrying the test leads. The WV-38A is attractively styled, with a rugged, lightweight, bakelite case. ^Included on wired instruments with serial numbers above 20,000, and on kits with serial numbers above 66,000 K.

Items Supplied with WV38A

1—Red Test Lead and Probe 1—Black Test Lead with Alligator 1—Slip-on Alligator Clip and Red Clip and Black Boot

Boot 1—Warranty - Registration Card 1—Instruction Book

(Batteries Not Supplied)

Available Accessories for WV-38A WG-297 High Voltage Probe WG-210 Resistor 900 Megohm for H.V. Probe (10 x multiplier for 5000

V. range) WG-211 Resistor 495 Megohm for H.V. Probe (100 x multiplier for 250

V. range) WG-270A Vinyl Carrying Case

3


Specifications Electrical

DC Voltmeter (at full scale) : Ranges 0 to .25, 1.0, 2.5, 10, 50, 250, 1000, 5000 volts Input resistance 20,000 ohms-per-volt Circuit loading 50 microamperes bleeder current Accuracy ± 3 %

AC Voltmeter (at full scale) : Ranges . . .." . . .0 to 2.5, 10, 50, 250, 1000, 5000 volts Input Resistance 5000 ohms-per-volt Circuit loading 200 microamperes bleeder current Accuracy ± 5 %

Frequency Response (reference 1000 cps) flat within *4 db from 10 cps to 50 kc on the 2.5, 10, and 50 volt ranges.

DC Current (at full scale) :

0 to 50 microamperes 0 to 1 milliampere

¥ ? o « M o 1 0 to 10 milliamperes K a n g e s • • ' " " ^ 0 to 100 milliamperes

0 to 500 milliamperes 0 to 10 amperes

Insertion Loss .0.25 volt Accuracy ± 3 %

DC Ohms: Ranges Scale Ends Center Scale Full Scale Currents

R X 1 0-2000 12 ohms 120 M A R X 1 0 0 0-200,000 1200 ohms M A R X 10,000 0-20,000,000 120,000 ohms 0.06 M A Accuracy ± 3 ° of pointer position for exact value

Internal Batteries: R X 1 SizeD Cell, 1% volts R X 100 Size D Cell , i y 2 volts R X 10,000 . .4 Penlite Cells in series with D cell, 7% volts

AF Output (at full scale) : Ranges 0 to 2.5, 10, 50, 250 volts Input Resistance 5000 ohms-per-volt Circuit Loading 200 microamperes Accuracy ± 5 %

Note : A n internally connected 0.1 *if D C blocking capacitor permits out

put measurements in presence of D C voltages.

4


Decibel Levels (Zero DB is 1 milliwatt in 600 ohms) : 2.5 V , range 10 V . range 50 V . range 250 V . range

- 2 0 to +10 D B - 8 t o + 2 2 D B + 6 t o + 3 6 D B +20 to +50 D B

( M a y be read on Output or A C positions)

Mechanical Specifications Dimensions—(less handle)

Height Width Depth Weight

. 6% inches

. 5x/4 inches :3Y$ inches 3l/2 pounds

Meter Scales There are five separate scales on the meter. The top black scale is

used when measuring Ohms. The second black scale is used to read D C voltages and currents. The two red scales are used when measuring A C voltages, the lower one being used only for the 2.5 V . range. The bottom scale on the meter is used for decibel measurements. A chart, located at the lower right hand corner of the scale for convenience, is used when making decibel measurements.

The Range Switch, located at the center of the control panel, has 12 positions. The Range Switch may be turned in either direction to obtain the function and range desired.

The Function Switch located at the upper left-hand corner of the panel has three positions, " A C " , " + D C " , and " — D C " .

To measure all A C Voltages and to make decibel measurements, the switch must be set to the " A C " position.

For positive direct current and D C voltage measurements, the switch must be set to the " + D C " position.

9 The " — D C " position reverses the polarity of the " — C O M M O N " and "+" jacks, permitting direct measurement of negative direct current and D C voltage. This switch position can also be used as a convenient means of reversing the polarity of the test leads when checking the front-to-back resistance ratio of electrolytic capacitors and many types of semiconductor devices.

Range Switch

Function Switch


Operating Section

Zero Setting of Pointer The pointer of the meter must indicate zero when the WV-38A is in

the normal operating position. If the pointer does not indicate Zero, the adjustment screw located at the lower center of the meter cover should be readjusted.

Use of Range and Meter Scales The meter scales on the WV-38A have been designed to provide

ease of operation and quick readability over a wide range of measurements. Scales have been grouped according to the type of measurement for which they are used.

Because of the wide number of measurement ranges provided on the WV-38A, it is often possible to take voltage or resistance readings on two ranges and scales. For greatest accuracy in voltage and current measurements, always use the range which wi l l provide an on-scale reading which is nearest to the full-scale point. For example: 48 D C Volts can be read from either the 50 Volt or the 250 Volt range. Because the 50 Volt range wil l provide a reading nearest the full-scale point, the 50 Volt range only should be used if a reading of best accuracy is to be obtained. This general rule applies to all A C and D C Voltage ranges. For resistance measurements, however, the range selected should be the one which provides a reading nearest the center of the scale, because the WV-38A provides the most accurate Ohms readings at mid-scale points.

For some measurements it wi l l be necessary to use a multiplying factor with the scale to obtain the correct reading. The required multiplication is indicated by the setting of the range switch. For example: when the range switch is set to the 1000 V . position for voltage measurement, the 0 to 10 scale is used, but the reading is multiplied by 100 times.

C A U T I O N :

When making voltage or current measurements, it is good practice to make a trial measurement at a higher range setting than is considered necessary, because repeated overload may destroy the meter movement or impair the accuracy of indications.

It is also good practice for personal protection to turn off al l power to the circuit under test when connecting or disconnecting the test leads. The power to the circuit under test must be turned off when in-circuit resistance measurements are made, otherwise damage to the W V - 3 8 A may result.

6


Figure 1. D-C Voltage Measurement

DC Voltage Measurement (See Fig* 1.) 1. Set the A C - D C Switch to the " + D C " or " — D C " position as required. 2. Set the Range Switch to a position considerably higher than the

voltage to be measured. 3. Plug the black test lead into the "— C O M M O N " jack on the control

panel. 4. Plug the red test lead into the "+" jack on the control panel when

the 2.5 V. , 10 V, , 50 V. , 250 V . or 1000 V. , range is used. 5. Connect the test leads to the voltage sourc** ^ be measured. 6. Reset the Range Switch to a position w ^ gives a suitable pointer

deflection. 7. Read the D C voltage from f 1 scale corresponding to the range

selected. Note: In rare applications where high energy rf is present, such as measur

ing dc "keep-alive" voltage on TR tubes in radar equipment, it may be necessary to disconnect meter-protection diodes CR3 and CR4.

Special .25 Volt, 1 Volt, and 5000 Volt Ranges Note: When using the .25 V and 1 V jacks, the Function Switch must be

set to the " + D C " position. Meter polarity must be observed by applying the red test lead to the positive circuit point and the black test lead to the negative circuit point.

8. To use the .25 volt range, set the Range Switch to the ".25" position, and plug the red test lead into the "+.25 V/50/*A" jack.

9. To use the 1 volt range, set the Range Switch to the "1.0 V " position, and plug the red test lead into the "+1 V " jack.

10. To use the 5000 volt range, set the Range Switch to the 5000 V position, and plug the red test lead into the " D C 5 K V " jack.


Figure 2. A-C Voltage Measurement

AC Voltage Measurement (See Fig. 2.) 1. Set the A C - D C Switch to the " A C " position.

2. Set the Range Switch to a position considerably higher than the voltage to be measured.

3. P lug the black test lead into the " - C O M M O N " jack on the control panel,

4. P lug the red test lead into the " + " jack on the control panel when the 2.5 V , 10 V , 50 V , 250 V , or 1000 V range is used. When the 5000 V range is used, the red test lead must be plugged into the " A C 5 K V " jack.

5. Connect the test leads to the voltage source to be measured.

6. Reset the Range Switch to a position which gives a suitable pointer deflection.

7. Read the A C voltage from the scale corresponding to the range selected.

8


Figure 3. D-C Current Measurements

DC Current Measurement (See Fig. 3.) 1. Set the A C - D C Switch to the " + D C " or " — D C " position as required. 2. Set the Range Switch to a position considerably higher than the cur

rent to be measured. 3. Plug the black test lead into the " — C O M M O N " jack on the control

panel for all ranges with the exception of the 10 AMPS range. 4. Plug the red test lead into the "+" jack on the control panel for all

ranges with the exception of the 10A and 50/iA ranges. 5. Connect the test leads in series with the current flow to be measured. 6. Reset the Range Switch to a position which gives a suitable pointer

deflection. 7. Read the D C current from the scale corresponding to the range

selected. 8. To use the 50/iA range, set the Range Switch to the "50aA" position,

and the Function Switch to " + D C " . Plug the red test lead into the "4-.25 V/50/*A" jack. Meter polarity must be observed by applying the red test lead to the most positive current connection and the black lead to the negative connection.

9. To use the 10 A M P range plug the black test lead into the "—10A" jack, and the red test lead into the "+10A" jack. On this current range the A C - D C Switch must be set to the " - f D C position, and the Range Switch set to the 10A position. Meter polarity must be observed by applying the red test lead to the most positive circuit connection and the black lead to the other circuit connection.


Figure 4. DC Ohms Measurement

Ohms Measurement ( See Fig. 4.) 1. Set the Function Switch to the " + D C " position. 2. Set the Range Switch to the appropriate position. 3. Plug the black test lead into the " — C O M M O N " jack on the control

panel. 4. Plug the red test lead into the " + " jack on the control panel. 5. Short the test leads together and adjust the Z E R O O H M S control

until the pointer indicates "0" (full scale clockwise). 6. Connect the test leads to the resistance to be measured. 7. Reset the Range Switch if necessary to a position which gives a suit

able pointer deflection. If this is necessary, repeat steps 5 and 6 before proceeding with step 8.

8. Read the resistance from the O H M S scale, and multiply by the range factor.

C A U T I O N : Low-current, low-resistance devices, such as thermocouples and meter movements, may be damaged unless a range above " R X I " is used, because the W V - 3 8 A applies up to 1.5 volts across the resistance under measurement when the range selector is set at " R X 1".

To facilitate checking the front-to-back resistance ratio of electrolytic capacitors and semiconductor devices, the test lead polarity can be reversed simply by setting the Function Switch to the " — D C " position.

10


Figure 5. Decibel Measurement

AF Output (Decibel) Measurement (See Fig. -5.)

1. Set the Function Switch to the " A C " position. 2. Set the Range Switch to a position considerably higher than the

decibel measurement to be made. 3. P lug the black test lead into the " — C O M M O N " jack on the control

panel. 4. P lug the red test lead into the " O U T P U T " jack on the control

panel. 5. Connect the test leads to the A C source to be measured. 6. Reset the Range Switch to a position which gives a suitable pointer

deflection. 7. Read the decibel measurement directly from the D B scale when

using the 2.5 V . range. When using the 10 V , 50 V , or 250 V range refer to the chart located at the lower right hand corner of the meter scale, for the decibel factor that must be added to the meter indication for the proper decibel measurement.


Figure 6. WG-297 High Voltage Probe

Accessory High-Voltage Probe (Available on Separate Order)

The WG-297 High-Voltage Probe, i n combination with a multiplier resistor, as illustrated in Fig , 6, extends the D C rating of the W V - 3 8 A to a maximum of 50,000 volts for use i n high-impedance circuits. The WG-210 Mul t ip l ie r Resistor, which has a resistance of 900 megohms, multiplies the 5000 V . D C range by a factor of 10 times. (I .E. 50,000 V . DC. ) Similarly the WG-211A multiplier resistor, which has a resistance of 495 megohms, multiplies the 250 V . D C range by a factor of 100 times. (I .E. 25,000 V . D C . ) These probes and multiplier combinations make possible measurements in T V high-voltage power supplies and other high-impedance circuits having inherently poor regulation.

Applications The W V - 3 8 A is designed to measure the significant characteristics

of electrical and electronic circuits. It wi l l measure the voltage, the current, and the resistance of a l l D C circuits. For A C circuits, the measurement is indicated as R . M . S . volts or decibels. The decibel ranges are based on a zero level of 1 milliwatt i n 600 ohms. Ei ther part of a mixed A C and D C voltage can be measured separately with the WV-38A. The A C voltage can be measured individually through the use of the output circuit, and the D C voltage can be measured directly through the D C voltage circuit.


Checking Capacitors The R X 10,000 range of the WV- 38A permits some indication of

capacitor leakage resistance. A good paper or mica capacitor under 1 id wi l l indicate above the 20 megohm mark ("2K") after the init ial surge required to charge the capacitor is completed. If the resistance indicated is less than 20 meg., the capacitor probably has defective insulation. The time required to charge the capacitor wil l vary with the capacity. The greater the capacity, the more the pointer wi l l swing and the longer it wi l l take for it to return to infinity. If the capacitor is shorted, the pointer wi l l not return to infinity. If the capacitor is open, there wil l be no initial pointer deflection. Very small capacitors wil l indicate only a slight deflection and a rapid return to infinity. Electrolytic capacitors, however, normally indicate some leakage, after charging. The amount of leakage is generally related to the capacitance and voltage rating. For example, a low voltage, high capacitance unit wil l indicate more leakage (lower resistance) than a high-voltage, low capacitance unit. When testing an electrolytic capacitor, the red lead must be connected to the positive and the black lead to the negative terminal of the capacitor, and the function switch on the WV- 38A must be in the " + D C " position.

Checking Rectifiers The resistance of copper oxide, selenium, silicon and crystal recti

fiers can be measured in both directions. The resistance measured should be quite large in one direction and very small in the opposite direction. The front-to-back resistance ratio can be checked easily by setting the Function Switch from " + D C " to " — D C " , thus reversing the polarity of the test leads.

Use of an Isolation Resistor In certain sensitive circuits in radio and T V receivers and other

I.F. or R . F . high-gain amplifiers, it is not possible to connect leads without disturbing the normal operation of the circuits. Usually, D C voltage measurements in such circuits requires the use of a V T V M with a resistor-isolation probe, such as an R C A VoltOhmyst. However, when the VoltOhmyst is not available, the W V - 3 8 A can be substituted, if a resistor is used in series with the instrument, clipped onto the end of the red probe. If an exact measurement is not required, almost any value of resistor, higher than the circuit impedence, wil l isolate the instrument so it wi l l not overly disturb the circuit. When an exact measurement has to be made, a resistor should be used which exactly multiplies the input resistance of the instrument so that the reading can be made on one of the higher scales. The following table gives values of resistors to be used:

Range Resistor Reading Multiplier Scale to Read

2.5 V 50 K 2 X 5 V 2.5 V 150 K 4 X 10 V 50 V 1 Meg. 2 X 100 V

250 V 5 Meg. 2 X 500 V


WV-38A VOM Circuit Description

Metering Circuit The WV-38A meter circuit for the A C Volts, D C Volts, and D C cur

rent functions consists of the calibrating potentiometer R22, connected in series with the 50/xA meter movement.

In the ohms function, the calibrating potentiometer is replaced by R25, the front panel Z E R O OHMS control.

Some models of the WV-38A have two special silicon diodes (CR3 and CR4) connected across the meter terminals to prevent damage to the meter movement due to accidental overload.

DC Volts The eight ranges of the D C volts circuit are obtained by adding suc

cessively higher, values of resistors in series with the meter circuit. The .25 V range is connected directly to the meter circuit. The voltage

divider network used for the remaining ranges is composed of R27, R l , R2, R3, R4, R5, and R29.

AC Volts The diodes CR1 and CR2, along with R20 and R21, form a full-wave

rectifier circuit, converting the A C signal input to pulsating D C voltage. The six A C voltage ranges, as with the D C voltage section, are ob

tained by using a voltage-divider network. The resistors in this network are RIO, R l l , R12, R13, R14, and R28. R24 is a 6K potentiometer for calibrating the low A C ranges. R23, also a 6K potentiometer, is for calibrating the high A C ranges.

DC Current The D C current ranges are obtained by switching the appropriate

values of shunt resistance across the meter circuit to maintain 50/iA full-scale deflection. The ranges and shunting resistors are listed below:

Range Series Resistors Shunting Meter

50/iA No shunt used 1 ma R6, R7, R8, R9, and R26 10 ma R6, R7, R8, and R26 100 ma R7, R8, and R26 500 ma R8 and R26 10 Amp R26

Resistance In resistance measurements, the ohms control, R-25, is connected in

series with the meter, and is used for calibrating or "zeroing" each range. In the R x 1 and R x 100 ranges, the 1.5V " D " cell battery is applied

to the circuit. In the R x 10,000 range, the four 1.5V penlight cells are also used, resulting in 7.5 volts. The battery voltage is applied to the meter circuit and shunt resistors of the particular range so that when the test leads are shorted, 50/*A of current pass through the meter, causing full-scale deflection.


When a resistor is placed across the test leads, current flow through the meter wil l be reduced in proportion to the value of the resistor, thus causing the pointer to deflect down-scale to the appropriate reading.

In the R x 1 range, R16 and R17 are in series with the meter circuit, and R19 is shunting the meter circuit.

In the R x 100 range, R17 is connected in series with the meter circuit, and R16 and R19, connected in series, shunt the meter circuit. R15 is in series with the 1.5V battery.

In the R x 10,000 range, R16, R17, and R19, connected in series, are shunting the meter circuit. R18 is connected in series with the batteries (7.5V).

The 1 amp fuse is connected in series with the — C O M M O N jack, and serves to protect the resistors used for ohms measurement against damage due to accidental overload.

Maintenance The WV-38A may be removed from its case simply by removing four

screws from the rear of the case. The meter, panel, laminated circuit board and batteries are removed as a complete unit.

The need for battery replacement is indicated when the instrument will not zero properly on the Ohms ranges. If it is not possible to zero the R X 1 and R X 100 ranges, the large " D " cell requires replacement. If it is not possible to zero the R X 10,000 range, the four penlite cells require replacement. It is generally good practice to replace all batteries when a replacement is needed.

The batteries are installed in the instrument as shown in Figure 7, above. It is important that the batteries are installed with the polarity exactly as shown in the illustration, and that the battery clips make proper contact with the terminals.


Resistor Replacement Almost al l of the resistors contained in the W V - 3 8 A are mounted

on the rear of the laminated circuit board, which simplifies troubleshooting and repair. When replacing a resistor, the defective resistor should be removed from the laminated circuit board and the holes in the laminated circuit board should be opened to accept the lead from the new resistor. The holes may be opened with the use of a toothpick or appropriate probe while the solder is melted. Care should be taken to prevent any short circuit to any other part nearby when replacing the resistor.

Fuse Replacement The fuse contained i n the W V - 3 8 A is used to protect the Ohms-

Mult ip l ier resistors against burnout due to accidental misuse (applying voltage to the leads when the Range Switch is in the " R X I " or " R X 100" positions). This fuse may be replaced by unsoldering the lead to the A C - D C Switch and clipping the other lead. The new fuse may be soldered onto the lead clipped from the defective fuse. Care should be taken to prevent any short circuit, and if necessary, a piece of insulating sleeving may be placed over the fuse to prevent a short circuit.

N O T E : A burned out fuse wi l l make the instrument inoperative dn al l functions in which the 4 4 — C O M M O N " jack is used.

DC Calibration If an accurate D C Current source is available, it is recommended that

the calibration potentiometer, R-22, be set using the D C Current function of the WV-38A, as follows: 1. Set the Function Switch to " D C ^ and the Range Switch to "1 M A . " 2. Connect the test leads from the " — C O M " and " + " jacks to a 1 Ma

current source. 3. Adjust R-22 so that the meter indicates 1 M A (full-scale deflection).

R-22 can also be adjusted using a D C voltage source, as described below: 1. Set the Function Switch to " D C " and the Range Switch to the "2.5 V "

range. 2. Connect the test leads from the " — C O M " and jacks to a 2.5 V D C

source. 3. Adjust R-22 so that the meter indicates 2.5 V (full-scale deflection).

N O T E : A fresh 1.5 V battery can be used to calibrate R-22 on the 2.5 V range. Connect the test leads to the battery terminals, and adjust R-22 to indicate 1.57 volts (157 on the 250 scale).

16


Rectifier Replacement

There are two small rectifiers located at the top of the laminated circuit board. If either, or both rectifiers become defective, the W V - 3 8 A wi l l give incorrect indications when measuring A C voltages. When replacing a rectifier, be sure to observe the polarity of the defective rectifier before removing. The new rectifier must be replaced in the proper polarity, and the A C voltage ranges must be recalibrated by adjusting variable resistors " R 2 3 " and "R24." T o recalibrate the A C ranges of the W V - 3 8 A , proceed as follows:

AC Calibration

1. Set the A C - D C Switch to the " A C " position. 2. Set the Range Switch to the "250 V " position. 3. Connect the test leads to a known A C voltage source of 250 V A C . 4. Adjust variable resistor "R23" unti l the meter indicates full scale. 5. Remove the test leads from the 250 volt A C source. 6. Set the Range Switch to the "2.5 V " position. 7. Connect the test leads to a known A C voltage source of 2.5 V A C . 8. Adjust variable Resistor "R24" unti l the meter indicates full scale. 9. Remove the test leads from the 2.5 V A C source.

Removing the Laminated Circuit Board

When it is necessary to gain access to the under-side of the laminated circuit board or to the parts located between it and the front panel; the laminated circuit board must be removed. T o remove the laminated circuit board, proceed as follows: 1. Set the Range Switch to the "2.5 V " position. 2. Remove the knobs from the A C - D C Switch and the Z E R O O H M S

control by pulling. 3. Remove the knob from the Range Switch by loosening the set

screw. D O N O T turn switch from its position. 4. Remove the three self-tapping screws which hold the laminated

circuit board onto the panel posts. 5. Remove the two hex nuts and washers from the meter studs. 6. Remove laminated circuit board, observing copper rings placed

between the board and the meter. D O N O T lose or misplace these copper rings as they function as the contacts from the laminated circuit board to the meter. When replacing the board, make certain that the copper rings are placed between the laminated circuit board and the meter, otherwise, the W V - 3 8 A wi l l not function properly. Also dress the interconnecting leads away from the " A P 5 K V " and D C 5 K V " eyelets and resistors.

:RCA Volt-Ohm-Milliammeter

Replacement Parts List WV-38A Volt-Ohm Milliammeter

When ordering replacement parts, include the stock number and description of the part, the instrument type. Parts without stock numbers are standard catalog items.

All parts should be ordered from your local RCA distributor.

Symbol No. Description S ^ k

Resistors 45K Ohms 1% %W . . . . . . 217743,

150K Ohms 17c % W 56483-A" 800K Ohms 1% y 2 W 93843 4 Megohms 1% %W 218881 15 Megohms 1% 1W 99317 22.5 Ohms 1% 1W (blue). 218815 2.0 Ohms 1% 1W (yellow). 218813 0.452 Ohms 1% 1W (red). 218812 238 Ohms 1% % W 218806 6200 Ohms 1% V 2 W 236084 37500 Ohms 1% V 2 W 218809 200K Ohms 1% % W 56733 1 Megohms 1% % W 208022 3.75 Megohms 1% 1W . . . . 218880 110 Ohms 1% % W 237613 1138 Ohms 1% % W 218807 21.85K 1% y 2 W 218808 117.7K 1% y 2 W 218810 11.5 Ohms. 1% 1W (green) 218814 5K 1% % W 209637 5K 1% % W 209637

Variable 6000 Ohms 225351 Variable 10,000 Ohms . . . . 219488 Shunt Assy. 10 A M P . . . . . 219489 15K Ohms \% % W 97761 20 Megohms 1% 2W 218816 80 Megohms 1% 2 W . . . . . . 218817

Meter

Meter 50 Microamperes including plastic case and scale 218818

Capacitor

Capacitor 0.1 M F D 400V

Symbol No. Description Stock

No.

R l R2 R3 R4 R5 R6 R7 R8 R9 R10 R l l R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22, R23, R24 R25 R26 R27 R28 R29

M l

CR1, CR2 CR3, CR4

F l

B l B2

SI S2

Rectifier

Crystal Diode Type IN87. 230099

Crystal Diode 230125 Fuse

Fuse Pigtail 3AG 1 A M P 250V 212492

Batteries Type D 1.5V VS-036 Type A 1.5V VS-034

Switches Range Switch 218877 Function Switch 218876

Miscellaneous

Panel—with eyelet assembly 218994

Case—(less handle assembly) 218993

Handle—(including clips and hardware) 219092

Printed circuit board (less parts) 219091

Battery holder (U shaped for penlight cells) 219179

Penlight Battery Clip Flashlight Battery Clip^. . 219178 Test Leads

Red, with probe 221711 Black 221712

Meter case, plastic, front and rear 218995

Knob pointer 1 inch . . . 213831 Knob small with mark . . 219486 Knob small no mark . . . 219487 Screw—Handle mtg 219093 Clip—Lead Holder

(on handle) 219094 Probe—Red Probe

and Tip 219107 CI

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18

he

ck i.

99

25

92

36 34

77 76

94

93

92

91

79

78

11 L2

)5 31 86 87 93

94

07

-COMMON

Ft 1 AMP.

1 Bt 1.5V

1000VOC

250VDC

50 VDC

10V DC

2.5V DC

+ 10A -10A

NOTES:-1. S1 SWITCH POSITIONS-MARKED ON SIA DRAWING

R27

_ 15K +iv DCQ V \ A r

POSITION RANGE 1 1000V/5000V 2 250 V 3 50V (.25V, IV, 50JJA) 4 10V 5 2.5V 6 500 MA 7 100 MA 8 10MA (10A) 9 1 MA 10 R X 1 11 R X100 12 R X 10000

+ .25V/50JJA DCQ-

OUTPUT

o AC5KV

O DC 5KV

o

- ct * .1 MFD

R28 > 20 MEG

2W

O

R29 SO MEG

2W

tOOOVAC

CR3

+ / M1 \50 jJA

CR4

H 4 -

. R22 ) 6K/

CAL

2. ALL SWITCH WAFERS SHOWN AS VIEWED FROM FRONT (SHAFT END OF SWITCH) 3. S1 SHOWN IN POSITION # 1 4. S2 SHOWN IN W+DCH POSITION 5. SWITCH CONTACTS

SHORT ARROWS INDICATE WIPER CONNECTION LONG ARROWS INDICATE CENTER RING CONNECTION.

6. ALL RESISTORS '/2 WATT, ± 1 % UNLESS OTHERWISE NOTED.

, R15 110 < R18

117.7 K

If)

ts id

Schematic WV-38A

NOTE: In some instruments RIO is 7.5 K, and R22, R23 and R24 are 4 K.

ItC/1

Printed in U.S.A.

Documents

operating and maintenance instructionsRCA Volt-Ohm-Milliammeter Safety Precautions For proper operation, the ground (black) lead of the WV-38A should be connected to the ground of